In some applications, it is not only important that heat sources such as integrated circuits be cooled, it is also important that the temperature gradient between any two heat sources be minimized. For example, one key parameter governing the radio frequency (RF) performance of a phased array radar system is the temperature gradient between heat sources, such as power amplifiers, in the transmit/receive (T/R) modules of the system. The power amplifiers in these T/R modules are mounted on a cold plate or heat sink which dissipates the heat from the power amplifiers. Because the distance from each power amplifier to the cooled edge of the cold plate varies, the power amplifiers which are located the greatest distance from the cooled edge of the cold plate (e.g., the interior mounted power amplifiers) operate at a higher temperature than the edge mounted power amplifiers.
But, in order to meet strict RF error tolerances, phased array radar designs require that any two power amplifiers operate within 4° C. of each other.
This requirement is due to the fact that the RF performance changes with temperature, with the gain changing approximately 0.1 dB/° C. and the phase changing approximately 0.8°/° C.
Typical prior art phased array systems employ liquid cooling of the cold plate with fluid couplings connected directly to the cold plate assembly of the transmit/receive integrated multichannel module (T/RIMM) to reduce the temperature gradient between power ampliers. Other prior systems attempt to reduce the temperature of the interior mounted heat sources by employing heat sinks with graphite and/or aluminum added to the heat sink which increases the thermal conductivity of the entire heat sink. See U.S. Pat. No. 6,075,701 incorporated herein in its entirety by this reference.
These prior art designs, however, exhibit several distinct disadvantages. Liquid cooling the cold plate requires fluid couplings which are prone to leak, are expensive, and have a high life cycle cost. Heat sinks or cold plates with added graphite and/or aluminum to increase the thermal conductivity of the heat sink or cold plate increase the size, weight, and cost of the device and moreover, do not meet the minimum temperature gradient requirements discussed above.